Forged in the Dark game that lets you use any official playbook from the Evil Hat books (eg Blades in the Dark, Scum and Villainy, Band of Blades, Iruvia) with a little massaging, a mosaic setting
one of my formative experiences in roleplaying was playing a Gamma World mutant in a game of regular D&D 4e set in Eberron thanks to a cosmic accident thanks to a congenial GM willing to work with me to convert stats back and forth, and I think combining games in a shared engine is genuinely a fun thing that should be done whenever possible
